The bane of an adolescent young man's existence. Usually happens during class, normally after eyeing an attractive girl. Extremely embarassing, and when you get one, you'll stick your hand in your pocket to tuck it into your boxers in a futile attempt to avoid discomfort/embarassment. In the worst cases, you'll end up coming in your pants.

Rob: Shit, man I was looking at Samantha in English class, and I got a damn boner, man!

1)an erect penis
2)what your boyfriend has when you are making out with him or just holding his hand
3)how big you wish your penis was all the time

1)"my penis was so fucking hard last night I had a major boner"
2)sally was making out with johnny and felt his boner poking her.
3)"Man I had a huge boner last night I wish my penis was that big all the time without all the blood in it," Johnny thought to himself.